Normal FloraNormal Flora
Definition
Normal flora is the mixture of microorganisms (bacteria and fungi) that are
regularly found at any anatomical site of human body like:
Skin , Eyes (i.e.Cunjunctiva), Nose (i.e. Respiratory tract), Mouth (i.e Human Oral Cavity)
Ears, Urogenetal tract, Elementry tract
Resident flora
* Acquired rapidly during & after birth
* Reflects age of person
* Changes continuously through out life
* Reflects nutrition of person
* Reflects genetics of person
* 90% is Staphylococcus. epidermidis; S. aureus, may be in moist areas
* Reflects environment of person
* Reflects sex of person
Sterile tissues
In a healthy human, the internal tissues such as:
Blood, brain, muscle, cerbrospinal fluid (csf.) are normally free of microorganisms.
Importance of The Normal Flora (Advantages)
1. They constitute a protective host defense mechanism by occupying
ecological niches.
2. They produce vitamin B and vitamin K in intestine.
3. The oral flora contribute to immunity by inducing low levels of circulating and secretory
antibodies that may cross react with pathogens
4. The oral bacteria flora exert microbial antagonism against nonindigenous species by
production of inhibitory fatty acids, peroxides, bacteriocins, etc
5. The normal flora may antagonize other bacteria through the production of substances
which inhibit or kill nonindigenous species.
(Disadvantages) of The Normal Flora
1. They can cause disease in the following:
a) When individuals become immunocompromised or debilitated.
b) When they change their usual anatomic location.
2. The oral flora of humans may harm their host since some of these bacteria are pathogens
or opportunistic pathogens
Estimation of the Normal flora
It has been calculated that the normal flora human body about 1012 bacteria on the skin,
1010 in the mouth, and 1014 in the gastrointestinal tract.
Normal Flora of the Skin
The most important sites are:
1. Axilla
2. Groin
3. Areas between the toes
The majority of skin microorganisms are found in the most superficial layers of the
epidermis and the upper parts of the hair follicles.
Important bacteria:
Staphylococcus epidermidis , Micrococcus sp.
Normal Flora of the Cunjunctiva
Corynebacterium sp ., Staphylococcus epidermidis
Normal Flora of the Respiratory Tract
A) The nares (nostrils)
Staphylococcus epidermidis , Corynebacteria
B) The upper respiratory tract (nasopharynx).
Non-hemolytic streptococci , Alpha-hemolytic streptococci
C) The lower respiratory tract (trachea, bronchi, and pulmonary tissues):
Usually sterile.
The individual may become susceptible to infection by pathogens descending from the
nasopharynx e.g.
H. influenzae ,
S. pneumoniae).
Normal Flora of the Human Oral Cavity
Oral bacteria include:
1. Viridans streptococci
2. Lactobacilli
The Normal Flora of The Ears
1. Staphylococcus epidermidi
2. Staphylococcus aureus
Normal flora of the Urogenital Tract
a) The anterior urethra
1. Staphylococcus epidermidis
2. Enterococcus faecalis
b) The vagina
1. Corynebacterium sp.
2.Staphylococci
Normal Flora of the Gastrointestinal Tract (GIT)
In humans, the GIT flora are influenced by:
1. Age
2.Diet
3. Cultural conditions
4. The use of antibiotics
Normal Flora of the Gastrointestinal Tract (GIT)
At birth
The entire intestinal tract is sterile, but bacteria enter with the first feed. The initial
colonizing bacteria vary with the food source of the infant.
In breast-fed
•
1. Bifidobacteria account for more than 90% of the total intestinal bacteria.
2 . Enterobacteriaceae
In bottle-fed infants
Bifidobacteria are not predominant. When breast-fed infants are switched to a diet of
cow's milk or solid food, bifidobacteria are progressively joined by:
1. Enterics
2. bacteroides
In the upper GIT of adult humans
mainly acid-tolerant lactobacilli
e.g. Helicobacter pylori
The proximal small intestine
1. Lactobacilli
2. Enterococcus faecalis
The flora of the large intestine (colon)
1.Enterococci
2. Clostridia